MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Dynamo Bolt - High tensile required?

Hi everyone,

Quick question...

Driving along quite happily. Speed not excessive when I heard a loud metallic 'ping' sound. Pulled over to find fan belt was loose and not engaging.

Carefully drove home. Lifted the bonnet to find that the bolt which mounted the Dynamo to the engine was gone! Thus loosing tension in the fanbelt. Looks like it either worked loose through vibration or sheered off.

Which comes to my question...
If this was thru vibration, would it be best to replace the bolt with a high tensile one?... or is this just overkill.

My assumption is that it is not a 'special' fixture. Was just a garden variety bolt/nut attachment.

I have attached an image to show you exactly where I am referring to.

Many thanks
Look forward to hearing from you soon.

Mark


Mark Duggan

I would think it was more likely to have worked loose and eventually dropped out than sheared. That bolt wouldn't be under great stress normally. Put a Nyloc nut on the replacement.
Mike Howlett

Mark-
A Grade 5 shouldered machine bolt will do nicely. I was going to suggest a nylock nut to make the assembly vibration-proof, but Mike beat me to it!
Stephen Strange

Thanks Mike. I didn't think of adding a Nyloc nut. Great idea.
Mark Duggan

I'm sure this is just a garden variety bolt. My car came from new with a flat and a spring washer here, spring washers must cost at leas 2p/100 so BMC wouldnt fit one if it wasnt needed.
Stan Best

Mark - When you replace the bolt and get the dynamo tightened into place, don't over tighten it. In fact, leave the belt quite loose so it doesn't put a lot of strain on the armature of the dynamo, causing the rear bushing to wear excessively. See the article, Keep Your Belts Loose in the Other Tech Articles section of my web site at: http://homepages.donobi.net/sufuelpumps/
Cheers - Dave
David DuBois

As a former fastener person (not an anorak!) the original bolt would have had a plain shank (length varied to suit the application)underhead. Many replacements will by now be (UK term) set screws i.e. threaded up to the head.(Cheaper & readily available for the non purist!)
Normal practice would be to fit a spring washer & spreader washer under the nut (or under the bolt head if going into a tapped hole), but a Nylok (use once!) & spreader washer is also good.
With Unified bolts/sets Code "R" equates to Metric 5.5 and Code "S" to 8.8. On a good quality bolt this will be marked on the bolt head together with the manufacturer's identifier (GKN/L(Linread)/AS (Armstrong) etc)
So there!
DG Harrison

Thanks for the tip Dave. I'll definitely use your advice on tightening the dynamo... and I'm about to print off your article to read. Cheers.

D G Harrison - Thanks for the info on the bolts. Every bit of advice is gratefully received.

Kind regards
Mark
Mark Duggan

This thread was discussed between 01/12/2010 and 02/12/2010

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now